Succinic acid and its derivatives are widely used as specialty chemicals for applications in foods, pharmaceuticals, and cosmetics.
The Glassner et al. U.S. Pat. No. 5,143,834 and the Datta et al. U.S. Pat. No. 5,168,055, disclose integrated processes for the production of succinic acid. These patents employed the anaerobic bacterium A. succiniciproducens which produces major amounts of succinic and acetic acids in approximately a 4 to 1 ratio. The Glassner et al. patent discloses that after conventional electrodialysis, water-splitting electrodialysis, cation exchange, and anion exchange the resulting final product contains 19.9% acetate and 79.6% succinate on a dry weight basis.
The elimination of the acetate in the fermenter broth would vastly improve the final succinic acid product since acetate is the major impurity in an otherwise highly purified product. One method of eliminating acetate would be to use a microorganism that produces less or no acetate. Aside from an improved electrodialysis product there are other possible benefits in having a microorganism that produces less acetate. These include reduced toxicity from acetate and an increase in succinate yield. The accumulation of acetate contributes to the cessation of growth and fermentation by the producing organism, and the effect is particularly pronounced at a low external pH (1). In addition, since A. succiniciproducens produces succinic acid only at the low end of its pH range (6.0-6.2), the elimination of acetate accumulation could extend the biocatalytic life of the A. succiniciproducens biomass. Furthermore, because it is necessary in order to increase the succinate yield to increase the amount of carbon flow in the succinate specific pathway, additional carbon could be diverted to succinate by strains which produce less acetate.
It would be advantageous to have a method for making a product containing more succinic acid and containing less acetic acid. It also would be advantageous to have microorganisms for use in such a method and a method of obtaining such microorganisms.